1. Field of the Invention
This invention relates to the monitoring of the waveform of cyclic movement, such as the breathing rate and/or the movement of the heart or parts thereof, within the thorax of an individual person or animal (such as a laboratory animal) in accordance with a doppler-shift in frequency of a microwave or radio-frequency signal passing into and out of the thorax of the individual.
2. Description of the Prior Art
The use of doppler-shift radar to monitor the breathing of an individual or, alternatively, in the field of echocardiography is known in the art. Such doppler radar extends from microwave radar scanners that are situated some distance from the individual and pick up reflections off an individual being scanned to doppler radar, operating at a microwave frequency or a lower radio-frequency, which transmits a predetermined-frequency signal into the body of the individual and receives reflections from moving internal organs of the individual. Further, there are known systems which, besides receiving transmitted reflections, also receive microwave signals transmitted through the thorax of an individual from a transmitter located on the opposite side of the thorax from the receiver. In this latter case, both a reference signal corresponding to the microwave signal transmitted into the thorax and the signal received after transmission through the thorax are applied through external wires as respective inputs to the same detector.
In principle, the monitoring of cyclic movement within the thorax of an individual in accordance with a doppler shift in frequency of a microwave or radio-frequency signal can employ either an antenna that is in direct contact with the skin of the individual or an antenna which is not in contact with the skin of the individual. A non-contact receiving antenna picks up scattered energy that follows multitudinous pathways within and around the body. This multipath propogation permits spurious doppler frequency shifts in the received signal arising from motions outside the body of the individual (e.g. motion from another individual or animal in close proximity to the individual, etc.). While direct-contact antennas minimize the scattered radiation problem outside the body encountered by non-contact antennas, use of such direct-contact antennas is often infeasible or, at least, undesirable.
One example of a case in which a direct-contact antenna is infeasable is in the monitoring of the breathing rate of an infant (particularly a premature infant) for the purpose of guarding against crib death. Another example is the case of a patient located in a recovery room immediately after the completion of an operation in which the patient has been anesthesized. In such cases, it is not practical to "wire-up" the patient or infant with antennas in direct contact with skin of the individual. Instead, it is much more practical to employ non-contact antennas situated adjacent to the thorax of the individual, such as located within a pocket in a gown or other garment covering the individual.
The present invention provides a practical way of employing non-contact antennas in the monitoring of the waveform of cyclic movement within the thorax or an individual person or animal in accordance with a doppler shift in frequency of a microwave or radio-frequency passing into, through, and then out of the thorax of the individual without being subject to the scattered field produced by moving objects outside the body of the individual.